Hung window assemblies generally include a window frame, a lower window sash, an upper window sash, a pair of window jambs, two sets of jamb pockets, and at least one window balance device for offsetting the weight of a window sash throughout a range of travel within the window frame. Block and tackle window balance devices use a combination of a spring and pulleys located within a channel to balance the weight of the window sash at any position within the jamb pockets.
In some block and tackle window balance devices, the channel containing both the spring and pulleys is attached to the window sash, and a cord, which connects the pulleys together, is attached to a jamb mounting hook that is connected to a side jamb. A disadvantage of this type of device is that the travel distance of the window sash is limited by some of the pulleys located within the rigid channel interfering with the jamb mounting hook that attaches the window balance to the window jamb.